I would be glad to help you, but...
I don't have Galaxy i5500, but I7500 and also not using original firmware from Samsung (custom ROM user). And this is the part of the forum for I7500.
But I can give you some advice.
Did you try by using a custom ROM based on CyanogenMod 7.2. Maybe you flashed a custom ROM with a buggy DSPmanager. So now try some other custom ROM. For more infos take a look
here.
Also if you can post your question there.
If you want to try yourself by using a menu:
look in [1], [3], [6] and [8] and post here their submenu.